Zacks "utilizes multi-factor proprietary selection rules to identify MLPs that may offer the greatest yield by assessing various factors, including yield, liquidity, relative value, and other factors. Each company is then sorted from highest to lowest based on its yield," according to the filing.

Following that screening process, the universe of possible constituents is whittled down to 25 and each receives a weighting of four percent within the index.

As investors have increasingly sought new avenues of yield, MLP ETFs and ETNs have soared in popularity. The largest MLP exchange traded products include Alerian MLP ETF (NYSE: AMLP) an the JPMorgan Alerian MLP Index ETN (NYSE: AMJ). Others include the Global X MLP ETF (NYSE: MLPA), the Yorkville High Income MLP ETF (NYSE: YMLP) and the Yorkville High Income Infrastructure MLP ETF (NYSE: YMLI).